I think Microsoft is in a weird position regarding the name of their consoles: they already have a well positioned brand, like Xbox, but if they just put a number for a new gen, they will look lazy and trying to copy the PlayStation naming style, and the "Xbox 4" will sound older than "PlayStation 5".
And their console is a traditional one, powerful and everything, but without a gimmick that could help to define the name and marketing, like Nintendo has done since the N64, so yeah, I think they need to create some kind of naming logic for their consoles.
As many have already said, they can build upon X being the flagship model and S the cheaper one, but dropping the "Series"